Technical Abstract:
Crop residue often has solar radiation reflectance properties that differ appreciably from those soils. Residue reflectance changes as the residue weathers and with wetting and drying. Prostrate residue on the soil surface also absorbs incoming radiation that would otherwise reach the soil. Through these combined effects, crop residue has the potential to significantly alter the surface radiant energy balance. The objective of this research was to measure the effect of corn (Zea mays L.) residue on reflectance and transmittance of shortwave and photosynthetically active radiation (PAR) under field conditions. Various radiation measurements were made 2 m above the field of standing corn stubble having approximately 80% residue cover. Incoming and reflected solar radiation were measured with LI-COR silicon cell pyranometers (LI-200SA, LI-Cor, Inc., Lincoln, NE). Solar radiation transmitted through the residue layer was measured with two tube solarimeters (TSL, Delta-T Devices, Ltd., Burwell, Cambridge, UK) positioned between the residue layer and the soil surface. Incoming and reflected PAR were measured with LI-COR quantum sensors (LI-190SA) and transmitted PAR was measured with a LI-COR line quantum sensor (LI-191SB). Approximately 18% of the incoming shortwave radiation was reflected by the corn residue/soil surface. For PAR (0.4-0.7 um waveband), the reflectance was only approximately 12%. The amount of radiation intercepted by the crop residue was proportional to the level of residue cover.